Various ion exchange materials, both organic and inorganic, are widely acknowledged as having the ability to remove certain metal ions such as lead from aqueous solutions. The use of organic ion exchange materials is popular in current carafe or gravity filter products. One of the disadvantages of organic ion exchange materials is that they swell when in contact with water while inorganic materials do not swell. The organic ion exchange materials are not stable at high temperatures. Most of the organic ion exchange materials are expensive and used in a packed bed form.
The use of inorganic materials such as crystalline zeolites and amorphous gels is much less popular. In the water treatment industry inorganics find use in lead removal, but appear to be in particulate or granular form. For example, it is well known that inorganic ion-exchange materials can provide the same function as organic ion exchange resins. Commercially available carbon block filters, made from granular activated carbon (GAC), commonly mix amorphous titanium-silicate powders with their GAC and polymer binders before forming. The amorphous titanium-silicate powders are used for lead and other heavy metal removal in drinking water. These powders are held in place by the polymer binders and the GAC.
There are some claims of inorganic ion exchange materials being attached to other support materials, such as carbon granules. However, the support in such cases is still a particle or granule itself. Unfortunately, the bonding between the ion exchange material and the granular carbon support has typically been quite poor, resulting in continual sloughing off of the ion exchange material. As a result, large amounts of water are needed to wash the filter before the water is clear enough for consumption.
There is never a guarantee that the water is completely free of ion exchange material. The continual sloughing off shortens the life of the device and may have adverse effects on the health of individuals drinking such treated water.
A common method for ion exchange purification is to run the feed solution through a column filled with the ion exchange material. In order to accomplish significant ion exchange, columns of considerable length are sometimes required. However, with increasing column length, the flow rate decreases. Also, such columns develop channeling of the feed solution, which decreases the ion exchange efficiency.
Accordingly, a need exists for efficient liquid purification devices in which the disadvantages of loose powder or granular or loosely bound materials are eliminated and in which the disadvantages of decreased flow due to channeling are eliminated.
The present invention provides such structured materials and methods.